Your situation sounds perfect for installing glass block. It obscures the view while still letting in the sunlight. It comes in several colors as well, so you could intermingle another color or two with the standard clear and come up with a pleasing design.

Depending on the size of the window you can use a shower curtain and hang it a cafe rod. This is also good so the curtains don't get ruined with water!

Go to your local glass company and ask for opaque or textured glass for a bathroom window.

They can change the glass in the frames for you, or you can do it yourself.

We have the same situation at our house. When we do remodel, the window will be removed and filled in so we can have a tub surround installed. You could add glass blocks, above the tub surround, or eliminate the window like we are going to do. If darkness in bath room is an issue, installing a solar tube in the ceiling is also an option.

Lowes has a product where you can apply a film to your window. It comes in several designs. You can put it over your exsisting window.

We have the same situation. I found window cling that goes onto the window to obscure anyone from looking into the window. That way we didn't have to replace anything. They used to only come in one kind of frosted styling, but I have seen them both at Lowe's and Home Depot, with beautiful flowers and even some that look like stained glass. Very easy to put on. Around $20 for one window.

All of the previous answers are great and I love the glass brick wall, but…the can get costly. I had this same problem in my downstairs bathroom and I bought a spray can of window frost. It is so easy,doesn't cost much and very effective. And you can spray the entire window or do a stencil. Worked great for me and if you don't like it or want a change in the future,it is easy to remove.